Drivers: hv: vmbus: Support kexec on ws2012 r2 and above

Drivers: hv: vmbus: Support kexec on ws2012 r2 and above

BugLink: http://bugs.launchpad.net/bugs/1558720
WS2012 R2 and above hosts can support kexec in that thay can support
reconnecting to the host (as would be needed in the kexec path)
on any CPU. Enable this. Pre ws2012 r2 hosts don't have this ability
and consequently cannot support kexec.

Signed-off-by: Alex Ng <alexng@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from linux-next commit 7268644734f6a300353a4c4ff8bf3e013ba80f89)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>